Process for laser hardening drilling bit cones having hard cutter inserts placed therein

Abstract

A medium to high carbon steel body of a roller cone for a drilling bit is machined to final dimensions, and is thereafter rendered absorbent to laser light by application of black paint or black etch. Holes for hard tungsten carbide or like inserts are drilled in the light absorbent steel body. The entire steel body, including the holes, is subjected to a laser treatment which, however, is effective to raise to above austenitizing temperature only the dark light absorbent surfaces. Walls of the insert holes, being shiny, reflect the laser light and are not effected by it. Rapid self-quenching of the laser heated surfaces results in a hard martensitic layer in the external surface, with a surface hardness of 57 to 60 Rockwell C units. The seal gland, heel, and spindle bore areas of the roller cones are hardened similarly by exposure to laser light. In an alternative process, the hard tungsten carbide or like inserts are press fitted into the holes before the laser treatment. The subsequent laser treatment does not affect the inserts adversely, because the inserts, too, have shiny light reflective surfaces, and therefore do not absorb the laser light.

What is claimed is: 
     
       1. A process for forming a tool having a hard cutter insert, the process comprising the steps of: forming a tool blank from a medium to high carbon hardenable steel, the tool blank having an external surface;   applying a coating to the external surface to render the external surface dark and absorbent to laser light;   after the step of applying the coating, forming at least one hole for the hard cutter insert, and affixing the hard cutter insert into the hole, the hard cutter insert having shiny light reflecting external surfaces, to provide a first intermediate tool blank, the first intermediate tool blank thereby including dark light absorbent surfaces and also reflective surfaces relatively unabsorbent to laser light;   after the step of affixing the hard cutter insert into the hole, bombarding the external surface of the first intermediate tool blank with a laser beam that is principally focused on the external surface of the first intermediate tool blank, the laser beam being of sufficient intensity and operated for sufficient time so as to austenitize an external layer in the light absorbent external surface of the first intermediate tool blank, the external surface of the hard cutter insert being out of focus when exposed to the laser beam; and   cooling the austenitized layer sufficiently rapidly to form martensite in the external layer of the light absorbent external surface, whereby the tool is obtained having a hardened external case.   
     
     
       2. The process of claim 1 wherein the step of cooling comprises cooling by self-quenching. 
     
     
       3. The process of claim 1 wherein before the step of bombarding with a laser beam, the tool blank has a surface hardness of approximately 40 to 42 Rc hardness units. 
     
     
       4. The process of claim 1 wherein after the steps of bombarding and cooling, the surface hardness of the tool is approximately 57 to 60 Rockwell C hardness units.